The present invention relates to a method and apparatus for producing para-aramid pulp and pulp made thereby.
The industrial demand for para-aramid pulp such as the poly(p-phenylene terephthalamide) pulp sold under the trademark Kevlar.RTM. by E. I. du Pont de Nemours & Co. has been steadily increasing. Due to high temperature stability, strength and wear resistance, para-aramid pulp is increasingly being used in brake linings and gaskets to replace asbestos with its known health risks. Para-aramid pulp is also being used in newly-developed papers, laminates and composites for applications requiring high strength and temperature stability.
Most para-aramid pulp is produced by first spinning oriented, continuous filaments of the para-aramid polymer in accordance with the dry-jet wet spinning process disclosed in U.S. Pat. No. 3,767,756 and then mechanically converting the filaments into pulp. However, the spinning of para-aramids is an expensive and complicated process. To describe the process briefly, the polymer is dissolved in 100% sulfuric acid to produce an optically anisotropic spin dope. The anisotropic spin dope is spun through an air gap under carefully controlled conditions into a coagulation bath. Typically, the spun filaments are also washed and dried before mechanical conversion into pulp. It is also generally necessary to use specialized fiber cutting equipment to cut the continuous filaments into uniform short lengths before pulping.
While attempts have been made to produce para-aramid pulp without first spinning fiber, a commercially feasible process for so producing para-aramid pulp suitable for current end uses has not been developed.